Polio

Until Salk and Sabin produced the first effective polio vaccine in the
early 1950's, every hospital had wards filled with survivors of paralytic
polio -- all of whom depended on "iron lungs" (a type of mechanical ventilator)
to breathe. Since the vaccine came into widespread and routine use, paralytic
polio has been almost unheard of in developed countries. In fact, polio has
nearly been eradicated, just as smallpox has; unfortunately, there has been a
recent resurgence of polio in parts of Africa, mainly in areas where vaccination
has been incomplete -- or worse, discouraged by leaders with no appreciation
of the risks of not vaccinating children.

The polio viruses (there happen to be three of them) are from a class known as
"enteroviruses", because they usually infect the intestines (at least initially).
For many people who are infected, a polio infection results in little more than
fever, aches and pains, and possibly mild
gastroenteritis. In others, though, the virus also attacks nerves that
control muscles, which leads to paralysis of those muscles. Before vaccines
were introduced, many polio patients became partly or completely wheelchair-bound
(Franklin Roosevelt was one famous example). In some cases the virus can attack
certain nerves which come directly off the brain rather than through the spinal
cord: this can paralyze the muscles of the face and throat, and obstruct
breathing. This, combined with paralysis of the chest muscles, often leaves
survivors dependent on ventilators.

Before Salk developed the injectable vaccine, polio epidemics were common
and usually happened about every 1-2 years. Since the vaccine became widely
used, polio has become quite rare in the United States and other developed
countries. The Sabin oral polio vaccine actually does a somewhat better job of
producing immunity -- for one thing, it stimulates the intestines to produce
antibodies, thus protecting against the virus at its point of attack -- and
it's a lot easier to give (who really wants shots when you can get a drop on
a sugar cube instead?). However, in about 1 out of 2,400,000 doses of the oral
vaccine a patient gets paralytic polio from the vaccine itself (caused when the
virus mutates into a form that is fully infectious), with 1 case of
polio after 750,000 first doses of vaccine (and that includes people
catching polio from someone else after receiving the vaccine but before starting
to develop immunity). Since 1979, the only cases of polio reported in
the United States were associated with the oral polio vaccine. Therefore, the
US Centers for Disease Control and Prevention
now recommend that we give only the injectable vaccine, and the
oral vaccine is no longer available in the United States or Canada. Oral
vaccine is still used in countries where polio remains prevalent; the risk of
getting polio from the vaccine is much less than the risk of catching polio from
someone else in those areas.

The vaccine, whether it is OPV or IPV, is usually given in four doses: at
age 2 months, at age 4 months, somewhere between ages 6 and 18 months, and
at age 4-6 years. If a child only received 3 doses of vaccine, and the
last one was at age 4 years or later, and they were all IPV or
all OPV, she does not need a fourth dose. However, if she received
some IPV and some OPV, she needs a total of 4 doses for complete protection
no matter how old she is now.

The immunity conferred by either vaccine may not be absolutely lifelong,
although the oral vaccine seems to provide longer-lasting protection. Since
polio is still prevalent in developing countries, it's sometimes a good idea for
adults to receive a booster dose of vaccine (usually IPV, since we don't routinely
carry OPV in the United States) before traveling to those areas. Your doctor can
help you decide whether you need a polio booster before a particular trip.

At the end of September, 2005, the Minnesota Department of Health reported a
case of polio in a 7-month-old girl. The child is Amish, and had received no
immunizations; she also has severe combined immune deficiency (SCID), which
makes her immune system unable to respond to many infections including
poliovirus infection. As of late October, when the
US Centers for Disease Control and Prevention reported this case in its weekly
report, 32 people living in her community had been tested for polio and 3 people
(brothers and sisters of each other living together, but not in the same household
as the infected girl) have tested positive. These three people had not been sick
and had normal immune systems, but none had been vaccinated against polio.

Analysis of the genes in the virus found in this girl showed that it is a mutation
of one of the three polioviruses in OPV. The amount of change between the little
girl's virus and the related OPV virus shows that the virus she has has been
replicating for about 2 years. Since she is only 7 months old, she must have
caught the infection from someone else, and since OPV has not been given to
anyone in the United States or Canada since 2000, the virus she has must have
started out as OPV given to someone in another country. (Neither she nor any of
her family have ever travelled abroad.) Since polio infections most often have
no symptoms, or at worse mild illness with fever, most people who might
be or have been infected wouldn't even know they had it. The reason we vaccinate
against polio is to prevent the unlucky 1 in 200 from becoming paralyzed, or worse.

Remember that IPV, being a killed-virus vaccine, cannot infect a patient. People
who have had all of their recommended doses of IPV are not susceptible to
polio, even the strain involved in this case.
I'm a bit of a libertarian, and I understand and honour the refusal of the Amish
to receive vaccinations. And, with SCID, this particular little girl likely would
not have become immune to polio even if she had received the vaccine. (Most likely,
she will need a bone marrow transplant before she has normal immune function.) On
the other hand, the reason for immunizations, whether for polio or for any other
disease, is to protect people from those diseases -- especially those
people, like this girl, who cannot defend themselves against the vaccine-preventable
diseases. If you doubt that vaccination against polio is necessary, go to the
CDC Web Site and read about this case. And if
your child is not up to date on immunizations, talk to his/her doctor about catching
up, and about any concerns you have about the vaccines.

PLEASE NOTE: As with all of this Web site, I try to give
general answers to common questions my patients and their parents ask me
in my (real) office. If you have specific questions about your
child you must ask your child's regular doctor. No doctor can give
completely accurate advice about a particular child without knowing and
examining that child. I will be happy to try and answer
general questions
about children's health, but unless your child is a regular patient of
mine I cannot give you specific advice.